This invention relates to a power transmission system of a marine propulsion unit and more particularly to an improved bevel gear transmission for such units.
It is well known to employ bevel gear transmission in marine outboard drives for transferring drive between two perpendicularly disposed shafts. Frequently, these drives include a reversing transmission that is comprised of a driving bevel gear on a first shaft and a pair of counter rotating driven bevel gears that are journalled on a second shaft and which may be selectively coupled for rotation therewith through a clutching mechanism. With respect to the counter rotating bevel gears, it has been the practice to position them axially upon the second shaft by means of a thrust bearing on one side and a thrust washer on the opposite side. However, such arrangements necessitate the use of a clearance in the system and this means that the bevel gears are not axially fixed upon their respective shaft. That is, the bevel gears may move axially along the shaft upon which they are rotatably journalled due to the clearances between the thrust bearing, thrust washer and the gear itself. Such arrangement are, of course, not completely satisfactory.
In the first instance, when the driven bevel gear is not clutched for rotation with the shaft it can move axially relative to the shaft under the action of the driving forces exerted on it by the intermeshing bevel gear. This axially movement of the bevel gear can give rise to noise. Furthermore, when the clutch is engaged, because the axially position of the bevel gear may move, additional noise, wear and possible other problems can result.
It is, therefore, a principal object to this invention to provide an improved power transmission system for a marine propulsion unit embodying bevel gears.
It is a further object to this invention to provide a bevel gear transmission for a marine outboard drive wherein the driven bevel gear is axially fixed relative to the shaft upon which it rotates under all conditions.
It is a further object to this invention to provide an improved arrangement for taking the lash out of the gear position of a bevel gear transmission.
In the type of transmission already described, it is common practice to employ a multiple disc clutch for clutching the counter rotating bevel gears to the shaft for establing a driving relation with the shaft. In my aforenoted co-pending application, this mechanism includes a hydraulic actuating piston for actuating the clutch. In addition, a spring is employed for releasing the clutch and moving the piston to its retracted position.
In accordance with a further feature of the invention, a clutch return spring is employed for also acting on the bevel gear associated with the clutch for holding the bevel gear against a thrust bearing so as to provide axial location for the bevel gear under all conditions.